1. Field of the Invention
The present invention relates to a teaching and playback method for a work machine and, more particularly, to such a method capable of assuring that construction equipment such as a hydraulic excavator performs a playback operation exactly as has been taught, even when a variation has occurred in the load on the machine. The method thus enables the machine to operate with improved accuracy even in such an event.
2. Description of the Related Art
Recently, it has often been the case with construction machines that they are required to perform work by repeating a certain operation. This particularly applies to a hydraulic excavator which is required, by the nature of its work, to perform repeated operations during, for example, earth excavation or loading. On the other hand, automatization of construction machines has been propelled by recent development in electronics, as shown in, e.g., Japanese Patent Application No. 149647/1988 (an application previously filed by the same applicant). A conventional teaching and playback method intended to automatize a construction machine of the above-described type has the following arrangement. During teaching, a locus of the work machine is taught by converting, into an electrical signal, the amount by which a work machine operation lever (hereinafter abbreviated to "work machine lever") is operated to move the machine along the locus, and storing the signal in a memory. During reproduction driving, the stored data is read from memory so that the machine performs a playback operation, which is an operation exactly the same as the taught operation.
With the conventional method, however, the following problem may be encountered in the event that, during a playback operation, the load on the machine should vary from the level upon which the teachings have been formulated. When the load on the machine has varied, particularly when it has increased from the above-mentioned level, there is the risk that the engine output may fall short. The engine rotational speed drops, causing a corresponding drop in the pump discharge. The insufficient pump discharge causes the work machine to move along a locus different from what has been taught. Thus, the machine operates with degraded accuracy. If a load variation occurs during multiple-actuator operation in which a plurality of work machine actuators are operated, there is a risk that the amount of flow supplied to the actuators may change, also resulting in movement of the machine along a locus different from the taught locus, hence, in degraded accuracy of operation.